Currently, with rapid development of information technologies, a capacity of a communications system needs to be further expanded to meet high-speed service requirements of user equipment (UE), and requirements of a mobile communications system for a bandwidth are also increasingly high. In order to meet the foregoing requirements, a device to device (D2D) communications technology emerges as the time requires. D2D communications is data exchange or a service that is directly performed between devices without forwarding by a base station.
When user equipments directly perform data transmission, transmission timing of user equipment that sends data is different from transmission timing of a base station. If user equipment that receives data determines, according to the transmission timing of the base station, a moment for receiving data transmitted from the user equipment that sends data, a timing synchronization deviation occurs between the user equipments. In addition, movement of UE is not limited in D2D communications; therefore, in D2D communications, a distance between UEs and a channel environment change with movement of UE, which also causes a timing synchronization deviation between the user equipments. As a result, the user equipment cannot correctly extract data, leading to a data decoding error, and reducing a system throughput.